Molecular Construction Using (C₃N₃O₃)^3– Anions: Analysis and Prospect for Inorganic Metal Cyanurates Nonlinear Optical Materials

Abstract

Molecular construction using good optically active microscopic units is vital to efficiently explore good nonlinear optical (NLO) materials, a type of important optoelectronic functional materials. In this work, we highlight the planar (C3N3­O3)3– anion, the main fundamental building block in inorganic metal cyanurates, as an outstanding candidate of building blocks for NLO materials. Several noncentrosymmetric metal cyanurates containing the (C3N3­O3)3– groups are studied by the first-principles calculations for the first time. It is shown that these materials possess wide band gaps (E g > 5.5 eV), high SHG coefficients (d 22 > 2 × BBO), and large birefringence values (Δn > 0.1) and thus have good potentials in the ultraviolet NLO applications. Moreover, the key role of the (C3N3­O3)3– groups to the good NLO performance in the cyanurates is elucidated. On the basis of the first-principles analysis, some possible searching directions of good NLO materials containing (C3N3­O3)3– groups are proposed.

The Sodium (Iso)Cyanurates Nax[H3–xC3N3O3]·yH2O (x = 1–3, y = 0, 1): A Key‐Series for Understanding the Crystal Chemistry of Metal (Iso)Cyanurates

“…A few years ago, only the crystal structures of two alkaline earth,, a few alkali, and some 3d‐transition metal isocyanurates were reported, all except one exclusively containing monobasic isocyanurate anions and crystallized from aqueous solution. Scientific interest in the topic has considerably risen since the discovery of the remarkable non‐linear optical properties of Ca 3 [C 3 N 3 O 3 ] 2 , focussing mainly on tribasic salts of divalent metal ions obtained via solid state methods . Recently, we accomplished to fuse these two branches of metal (iso)cyanurate chemistry within a broad structural and thermal study of alkali and alkaline earth isocyanurates by successfully preparing the full range of mono‐, di‐ and tribasic (iso)cyanurate salts directly from aqueous solution …”

“…In that preceding study we encountered a variety of structural motifs, ranging from the well known isocyanurate ribbon uniformly found for monobasic salts to isocyanurate dimers and chains for dibasic salts as well as columns for tribasic salts, the latter of which are also known from various compounds synthesized via solid state approaches . In order to shed light on the relationship between degree of deprotonation, crystal water content and formed structural motif, we looked for a series of salts which does not incorporate other chemical species except metal cation, (iso)cyanurate anion and water, as it is well known that the structural pattern is mainly governed by intermolecular hydrogen bonds,, and found the Na x [H 3– x C 3 N 3 O 3 ] · y H 2 O series.…”

Cs3Na(H2C3N3O3)4·3H2O: A Mixed Alkali‐Metal Hydroisocyanurate Nonlinear Optical Material Containing π‐Conjugated Six‐Membered‐Ring Units

“…This is favorable for obtaining stronger π‐conjugated interaction in the (H 2 C 3 N 3 O 3 ) – 6‐MR than that in the (B 3 O 3 ) 3– 6‐MR. Accordingly, it is expected that the microscopic susceptibility of (H 2 C 3 N 3 O 3 ) – groups would be larger than that of (B 3 O 6 ) 3– units …”

“…For a planar π‐conjugated group, there are two key parameters to determine its degree of conjugation, namely, bond length and the number of conjugated p π electrons. The degree of conjugated π‐bond will increase with the shortened bond and improved p π electrons, thus inducing enhanced second‐order susceptibility and SHG response . Based on the theoretical analysis, our group first proposed that cyanurate six‐membered ring (6‐MR) (C 3 N 3 O 3 ) 3– unit can be used as an excellent constructing block for ultraviolet NLO materials.…”

“…Comparing with the isoelectric (B 3 O 6 ) 3– group, (C 3 N 3 O 3 ) 3– group shows a shorter interatomic distance, stronger p π –p π conjugated interaction, and additional electron‐populated p orbitals from the C atoms. Therefore, the compounds containing (C 3 N 3 O 3 ) 3– 6‐MR groups exhibit not only larger linear polarization susceptibilities but also stronger SHG responses . Furthermore, due to the shorter interatomic structure, the cations with smaller ionic radius are needed to combine with the cyanurate anionic groups.…”